Recent events and a perceived increased threat from terrorist activities have resulted in an increased need to be able to screen the contents of bottles and similar containers which passengers may wish to carry onto an aeroplane or into a similar security sensitive environment. Such screening should be able to identify whether the contents of a container pose a threat to security, for example containing substances which could be ingredients for explosives, toxic, or otherwise unauthorised. Moreover, such screening needs to be rapid, avoiding taking samples out of relevant containers while still providing accurate results and a very low incidence of false alarms.
Raman spectroscopy is a known technique for determining characteristics or composition of materials, and has excellent chemical sensitivity, although is largely restricted to measurements of surface materials. Raman scattering occurs when a photon is inelastically scattered within a medium, changing the frequency of the photon by typically a few hundred to a few thousand cm−1 according to a spectrum characteristic of the scattering material. Although chemically specific, Raman scattering is very weak, and the spectral signal is easily swamped by fluorescence. In the case of the contents of a glass, or especially a plastic container, the relatively weak Raman signature of the typically liquid contents is often likely to be badly swamped by the much stronger signature of the container.
There are many other applications in which Raman spectral determination of characteristics within a container would be beneficial, but are at present hampered by the above problems, including for example the determination of beverage content, especially alcohol content, either on a production line or in a production, distribution or retail context.
The invention seeks to address the problems of the related prior art.